Tower for a wind power station

ABSTRACT

Disclosed is a tower for a wind power station comprising a machine pod disposed on the tower and a rotor mounted on the machine pod so as to be rotatable about an essentially horizontal axis. Said rotor is provided with at least one blade. The tower is composed of a tubular upper section that is connected to a lower section which is embodied as a lattice tower in a transition zone. The lattice tower encompasses at least three corner posts. The upper tower section forms at least one sixth of the entire tower. The cross section of the lower tower section below the transition zone is greater than the cross section of the upper tower section while the transition zone is configured such that the cross section of the lower tower section is adjusted to the cross section of the upper tower section so as to optimize power flux.

BACKGROUND OF THE INVENTION

Modem wind-driven power-plants are predominantly designed to rest ontubular towers, in particular steel tube towers, because this design,termed shell de-sign, is the simplest and most economical. Regardinglarge wind-driven power-plants having rotor diameters of more than 70 mand towers of heights in excess of 80 m, their output power being morethan 1.5 megawatt, the critical engineering limitation is the requiredtower diameter at the tower base. Towers of diameters larger than 4.3 mcan be transported only with difficulty because frequently the clearanceunderneath bridges would not allow going through the underpass. Moreoverthe total length and weight of such towers demands subdividing them intoseveral tower sections that are bolted to each other by annular flanges.In addition to transportation costs, such large annular flangeconnection means entail considerable costs when very large wind-drivenpower-plants (3-5 Mw) are involved.

In view of the difficulties in transportation, concrete towers are usedincreasingly, being manufactured either at the erection site of thewind-driven power-plant or else consisting of smaller components thatwill be bonded and braced together. Both types of towers however entailhigher manufacturing costs than tubular steel towers. As a resulthybrids of steel pipes and concrete are sometimes built, of which theupper tower is as much as possible a steel pipe tower and only the lowertower segment, of which the diameter is too large for transportation, ismade of concrete. However the transition zone between steel tower andconcrete tower entails complex engineering and high costs.

Furthermore, lattice towers called power pylons up to 114 m high arealready in use for large wind-driven power-plants up to 114 m high andallowing outputs up to 2 Mw. Besides the advantage of problem-freetransportation, such towers however also have the critical drawback of amuch larger horizontal expanse than a comparable steel tube or concretetower, frequently raising the problem of the required safe distancebetween the rotor blade tip and the tower (blade clearance). If in theevent of a storm, if the rotor blade were to be excessively bent out ofshape, there would be danger of contact with the tower and direconsequences for the entire edifice.

On the other hand, the larger horizontal expanse of the lattice towerallows materials to be saved. This advantage is known in theconstruction industry and saves on total weight and hence lowers initialcosts. On the other hand, this economic advantage is negated in generalby the tower maintenance costs required over a service life of 20 years.Illustratively, the dynamically highly stressed towers of thewind-driven power-plants must be checked periodically, and suchmaintenance at the lofty heights of the lattice towers is dangerous,time-consuming, physically exhaustive and must be carried out by highlyskilled specialists.

It is known from the German patent documents DE 736,454 and DE 198 02210 A1 that the tower may comprise an upper and a lower segment, thelower one being a lattice tower and the upper one being tubular.

Such designs suffer from the drawbacks of requiring very demandingengineering work at the transition zone between the shell construction(tubular tower) and the framework construction (lattice tower). As aresult, as regards extant lattice towers for wind-driven power-plants,in general only a tubular stub, the so-called “pot”, hereafter “stub”,will be inserted directly underneath the equipment nacelle to implementthe transition to the equipment nacelle fitted with an annular flange.In such designs the transition is implemented in general by typicallybolting four corner posts of the lattice tower by means of junctionplates or the like directly and from the outside on the stub. Thisdesign works because the tower is directly underneath the nacelle andthereby experiences only relatively low bending forces. In such adesign, substantially only the horizontal rotor thrust acting as atransverse force on the tower need be transmitted. Farther below, wherethe tower is primarily loaded by the rotor thrust bending torquegenerated by the leverage of the tower length, such a design becomesuneconomical.

BRIEF SUMMARY OF THE INVENTION

The objective of the present invention is to design a tower for largewind-driven power-plants in a manner to eliminate the drawbacks of thestate of the art, in particular regarding transportability, economics,maintenance and blade clearance.

In a manner known in the state of the art, the tower is fitted with anupper tubular tower segment and with a lower tower segment which, beinga lattice tower, is fitted with at least three corner posts. The twotower segments are joined to each other at a transition site, thedimensions of the upper tower segment being substantially smaller in thetransition zone than the dimensions of the lower tower segment.

In the present invention, the upper tower segment constitutes at leastone sixth of the entire tower. This feature offers the advantage that anadvantageous standard design may be used in the upper tower region

Furthermore, the torsion loads in the upper tower region are much higherbecause of its lesser cross-section than in the lower tower segment.Because a tubular tower exhibits high resistance to torsion, the torsionforces can be absorbed better, for instance using a lattice tower.

As already mentioned above, the transition zone from the lower towersegment to the upper one is problematical. The reason is that the forcesmust be transmitted from the tubular cross-section of the upper towersegment to the three or illustratively also four corner posts of thelower tower segment. The simplest solution would be, for instance, aplate to which the upper and lower tower segments would be affixed.However, such a plate would have the drawback of perforce being verylarge to withstand such forces and thus would also be commensuratelyexpensive.

While the present invention also provides that the lower tower segmentcross-section underneath the transition zone be larger than that of theupper tower segment, on the other hand, it does design the transitionzone in a manner to optimally match the cross-section of the lower towersegment to that of the upper segment as regards the distribution offorces. In this manner, the present invention offers the advantage of atransition zone where the force distribution passing from the uppertower segment to the lower one is optimized and that thereby the need tooversize the entire transition zone has been eliminated.

The synergy of the above features of the invention leads to an optimallydesigned tower. In its upper segment, the tower of the present inventionis a standard tower. As regards the lower tower segment, which forinstance because of its dimensions no longer can be designed as atubular tower because of no longer being transportable, it will be alattice tower. Using a lattice tower, moreover, offers a great advantagewith respect to an offshore wind-driven power-plant, namely that itseffective surface of wind incidence is less than that of a tubulartower. The advantageously matched transition zone leads to a latticetower segment of which the corner posts and strut means are thinner,allowing reduction of the tower weight and related costs, which are asubstantial part of the total cost of the wind-driven powerplant.

Relative to the tower axis, each corner post may subtend a slantselected in a manner that in a conceptual extension of said cornerposts, their longitudinal axes will cross each other at a virtualintersection point. Advantageously, the tower of the present inventionshall be configured in a way that the virtual intersection point of thecorner posts shall be situated in a region, above the transition zone,that extends upwards or downwards from the nacelle by a third of thetower length because in that manner the corner posts are loaded only byperpendicular forces but not by bending.

In general, lattice towers are fitted with strut means between thecorner posts to additionally withstand forces. By configuring theintersection point in the upper region of the wind-driven power-plant,the invention channels the force distribution predominantly through thecorner posts and consequently the force distribution in the strut meansshall be at a lesser level. In this manner the applied loads to thestrut means are advantageously minimized and, therefore, may be mademore compact, so that again the welding seam volume at the legconnections is advantageously reduced (cost savings).

In one advantageous embodiment mode of the invention, the transitionzone is configured in a way that the cross-section of the lower towersegment tapers toward the cross-section of the upper tower segment andthat, in an especially advantageous manner, this taper shall run along alength corresponding at least to the lower tube radius.

In further advantageous embodiments of the present invention, thetransition zone is constituted by a transition unit designed in a mannerthat the horizontal tower expanse in its lower segment shall besubstantially larger than that in the upper segment. Actually, thesubstantial kinks so entailed do conflict with present buildingregulations because, especially as regards shell construction, any kindof kinks will result in increases in forces that weaken the supportingstructure. However, by resorting to the steps defined in the dependentclaims, these indisputable drawbacks of the two kinks in the design ofthe invention can be negated or the kinks may be avoided entirely inorder to fully make use of the advantages of the design of the presentinvention.

Regarding the state of the art, such kinks arising in shell constructionare known only in very small wind-driven power-plants wherein forceoptimizing has not yet been a substantive factor. Instead the emphasisin manufacture has been to exploit the possibility of simply andeconomically connecting tubes having diameters readily available on themarket. Regarding such small equipment (less than 300 Kw output), extantshort tubular towers were deposited by means of strongly conicaladapters on tubular lower parts of larger diameters.

Regarding modern wind-driven power-plants with outputs larger than 1 Mw,only tubular towers susceptible to slight kinking (maximum: 5-8°) areeconomical in the state of the art, such kinking basically being locatedrelatively close to and underneath the equipment nacelle. Such designsillustratively discussed in European patent document EP 0 821 161 areknown as =37 doubly conical towers” mainly allowing use of a largeaffixation flange at the connection site to the equipment nacelle andthey serve to match the natural component frequency to requirements.

In a further advantageous embodiment of the present invention, thetransition between the upper and lower tower segments advantageouslyshall be situated (where called for directly) underneath that horizontalplane which is defined by the rotor blade tip when the rotor bladepoints vertically down. This design allows avoiding, in a simple manner,all known drawbacks of the state of the art.

The upper tower segment being tubular, the requirement of slendernessand previously unattained economy is met, furthermore simple maintenancewith weather-sheltered ascent means and working space also are criticaladvantages at such a great height. The moment the size of the tubulartower reaches its transportation limits, a lattice tower is inserted inthe lower tower segment underneath the plane of the blade tip. Thelattice tower, on account of its considerably larger horizontal expanse,provides substantial savings in material and hence greater economy. Themaintenance problem is less critical in the lower tower segment becausethe state of the art already makes available cherrypickers allowing themaintenance personnel to access in simple and comfortable manner thelower tower segment.

Another drawback of lattice towers, namely that icing in cold weatherconstitutes a substantial additional weight on account of the largesurface of the lattice-work, is substantially reduced in the presentinvention in that said additional weight only acts on the lower towersegment which is much less critical statically and dynamically.

Accordingly the transition zone is configured at a distance from therotor axis which may be from 1.0 to 1.6 fold and in particular 1.0 to1.3 fold the rotor radius.

To allow transporting the transition unit, the upper region of the unitshall be designed in an especially advantageous manner whereby, duringassembly of the wind-driven power-plant at the site of erection that theunit shall be affixed, preferably in a detachable manner, to the uppertower segment.

Again the lower region of the transition unit is advantageously designedto be connected by a preferably detachable affixation means to eachcorner post of the lattice tower.

In addition to the corner posts, several strut means also may beadvantageously screwed onto the lower region of the transition unit.

As found empirically in steel tube/concrete hybrid towers, the flangeconnection to the tubular tower must be considered as being especiallycritical.

Accordingly, an especially advantageous embodiment mode of the presentinvention provides that the detachable connection between the upperregion of the transition unit and the upper tower segment is fitted witha two-row screw flange situated preferably at the inside of theconnection site and a matching T-flange configured at the upper towersegment.

Fitting said connection site with a large, double row flange, moreover,offers the advantage that the flange simultaneously acts as a bucklingbrace for the excessive forces deflected at the outer contour kink. Inthis manner, the excessive forces caused by buckling are partly buteffectively reduced.

Advantageously, the lower region of the transition unit comprisesconnection sites for plate-junction affixation to the lattice tower'scorner.

Because the upper tower applies a considerable additional weight on thelower lattice tower, the corner posts of the lattice tower areadvantageously in the form of a hollow construction shape in order toprevent kinking caused by the loads from the tubular tower.

The transition unit design is further very advantageous in that thefinished height of the transition unit remains within the admissibletransportation height. As a rule, the maximum shipping height in Germanyis 4.3 m because of the limited clearance under overpasses, though goods5.5 m high may still be transported along selected routes.

If on account of size, the transportation of the transition unit in onepiece should be impossible—as regards very large wind-drivenpower-plants (about 3-5 Mw output)—another embodiment of the presentinvention provides in an advantageous manner that the transition unitshall be built in at least two sub-units preferably detachably connectedto each other at the connection site. Connection then may be carriedout, for instance, advantageously by means of screw flanges or brackets,though welding together the sub-units at the site of erection also maybe an economical solution when the connection sites are situated inlow-load zones.

In this respect the transition unit may be sub-divided in an especiallyadvantageous manner by a vertical partition plane into at least twosub-units. Subdivision into a number of sub-units corresponding to thenumber of lattice tower corner posts is especially economical formanufacture.

In another advantageous embodiment of the invention, sub-division of thetransition unit shall be in at least one horizontal partition plane.

Regarding especially large wind-driven power-plants, both types ofsubdivision obviously may also be combined.

In one advantageous embodiment of the present invention making full useof the maximum admissible height of transportation, the design of thetransition unit or of its sub-units is such that, by means of adapterelements mounted on the extant connection sites or on those especiallydesigned for this embodiment, the unit can be transported on alow-loader trailer.

Depending on the size and weight of the transition unit or sub-unitstherefore, transportation of several transition units or sub-unitsconnected to each other directly or indirectly (by adapter elements)also is provided-for on low loader trailers. Such a procedureillustratively offers the feasibility to screw together the sub-units ofan excessively high two-part transition unit at the (half) annularflanges and then keep them prone in order to stay within the permissibletransportation height on a low loader trailer.

The transition unit may be designed in an especially efficient manner inanother embodiment of the invention by being fitted with a wall andbeing built as a shell.

In an especially advantageous manner, the basic shape of the transitionunit substantially corresponds to a markedly conical tube of which themean wall slant relative to the center axis is larger than the wallslant of the lower region of the lattice tower and/or than the slant ofthe upper region of the lattice tower corner posts.

In this respect the mean slant is defined as the angle subtended betweenthe vertical (or also the center line) and a conceptual line from themaximum expanse in the upper region of the transit unit to the maximumhorizontal expanse in the lower region.

In order to carry out in an especially advantageous manner thepronounced increase of horizontal tower expanse of the invention, themean slant of the transition unit wall relative to the center axisshould be at least 15, preferably more than 25°.

As regards the basic shape of the transition unit being a conical tube,arbitrary tube cross-sections may be used, namely triangular, square,highly polygonal (for instance 16 corners), and also circularcross-sections. The invention also explicitly includes conical tubes ofwhich the cross-section varies with length.

An especially advantageous embodiment mode provides in this respect thatthe transition unit's cross-section shall smoothly change from beingsubstantially circular in the upper region into a substantiallypolygonal cross-section, preferably triangular or square, in the lowerregion. “Circular” in this context also may denote being highlypolygonal, for instance containing 16 corners.

If the connection to the tubular tower is implemented by an annularflange, this flange may smooth the transition for instance from a16-corner transition unit to the circular tubular tower.

If at least the lower portion of the tubular tower is also polygonal,affixation can be carried out in a problem-free manner using junctionplates. If the slants of the transition unit's side surfaces to thetubular tower wall vary, an additional buckling brace may be used ascalled for.

In an especially advantageous manner, savings in material and weight canbe attained by fitting the transition unit wall with at least oneclearance. By resorting to skillfully shaped clearances, the forcedistribution may be improved relative to the design devoid ofclearances. This feature applies in particular to archway-shapedclearances running from corner posts to corner posts.

Further optimization of the force distribution is attained by rib-shapedor door-frame like bracing at the edges of the arch-shaped clearances.

Advantageously, horizontal supports are configured between the cornerposts of the lattice tower in the lower region of the transition unitfor the purpose of increasing the latter's rigidity, said supportsjoining to each other the adjacent corner posts and/or diagonallyopposite corner posts.

These horizontal supports may be joined integrally to the transitionunit or, in an especially advantageous manner, they may be affixed bythe junction plate connection between the transition unit and the cornerposts.

A further advantageous embodiment mode of the present inventionincreases the transition unit rigidity by a configuration of ribs in atleast four corner posts to rigidify the connecting lines of diagonallyopposite corner posts.

In an especially advantageous embodiment, the transition unit is made bycasting.

The inherent shaping versatility of cast components allows, therefore,to avoid extreme forces at the kinks by providing gentle, roundedtransitions.

An especially effective design, taking account of force distribution,calls for the transition unit's wall annulus to be convex when seen invertical cross-section, this feature allowing especially gentletransition from the flange in the upper region to the corner posts inthe lower region.

In particular, the slant of the connection sites in the transitionunit's lower region should be designed in an especially advantageousmanner so that it corresponds to the slant of the lattice tower's upperregion corner posts.

Construction using cast components also is especially advantageous withmulti-part transition components exhibiting vertical partition planesbecause illustrative 4 identical cast components can be assembled intoone transition component (economy of large numbers). Casting materialsused for the casting embodiment modes illustratively are steel castingmaterials or granulated graphite cast irons, for instance GGG40.3.

If only a few towers of the invention should be built, the transitionunit design by welding will be especially advantageous because then thehigh costs of casting are avoided.

In the state of the art, the transition to the concrete pedestalfrequently is also implemented by T-flanges and therefore a furtheradvantageous embodiment of the present invention provides makingavailable a modular construction sequence of towers using thehybridization concept of the present invention, whereby an extanttubular tower (for instance an 80 m tower for a 1.5 to 2.5 Mw machine)is deposited by means of the transition unit onto different lowerportions (for instance 30, 50 and 70 m high) in the form of a latticetower in order that, depending on site, total tower heights of 110, 130and 150 m are attained. In this manner, even heretofore uneconomicalinland sites may become available for economic wind power.

In a further advantageous embodiment of the present invention, the lowertower segment in the form of a lattice tower comprises severalsuperposed floors where each floor always includes the corner posts andat least one bracing running diagonally between the corner posts.

In a further advantageous embodiment of the present invention, the slopeof the diagonal strut means is identical at all floors and as a resultof this identical identity, the connection points between the legs andthe strut means are also made identical. This design offers theadvantage that identical nodes may be used to connect the corner postsand the strut means. Tower design is advantageously optimized in thismanner. Heretofore the corner posts and strut means were matched to eachother at assembly and then were welded in an expensive manner.

Compared to welded junctions, cast junctions may be made significantlymore compact and hence more economically. To attain sufficient strength,welded junctions must in general be designed so that the weld seams donot intersect. As a result, the junctions frequently must be stretchedin the zone of the tube transitions, and this requirement does not arisein cast junctions. Both corner posts and diagonal struts, preferablystandard tubular shapes, for instance used in pipeline construction, maybe used between the junctions for further improvement in economy.Connection may take place by means of screw flanges or by welding.

Using identical junctions offers the advantage that they can bepre-fabricated and that the corner posts and strut means during towerassembly need only be inserted into the junctions and be welded orscrewed tight. This feature is a substantial simplification in the workentailed during lattice tower erection. Furthermore, substantial savingsare made on account of mass-producing identical junctions.

Especially as regards offshore power-plants comprising a lattice tower,additional tubes must be provided to lay the cables connecting to theelectric grid. On account of the waves, such additional tubes presentadditional stressed surfaces in an offshore power-plant, entailingadditional loads on the lattice tower. Accordingly, an advantageousembodiment of the present invention provides that, to secure reducedwave loading, the cables used to hook up the wind-driven power-plant tothe external electric power supply be placed in the corner posts of thelattice tower segment. In a further advantageous design of theinvention, cable protecting pipes are pre-positioned in the corner poststo receive said cables. Said protective pipes advantageously are made ofplastic and allow pulling the cables through them once the tower hasbeen erected and anchored on the sea bottom.

Further features, advantage and details of the invention are disclosedin part by the description below and are partly made plain by it orresult from the practical application of the invention. Two embodimentmodes of the invention are described comprehensively. It is understoodthat other embodiment modes may be used and that alterations may beintroduced without thereby transcending the scope of the presentinvention. Accordingly the following comprehensive description must notbe construed narrowly, in particular details of both embodiment modesalso may be interchanged at will.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wind-driven power-plant of the state of the art,

FIG. 2 is an overall view of the tower design of the present invention,

FIG. 3 shows a detailed view of one embodiment mode of the transitionunit of the present invention,

FIG. 4 is a detailed view of another embodiment mode of the transitionunit of the invention, and

FIG. 5 is the geometric development of the wall of the transition unitof FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a wind-driven power-plant of the state of the art where thesupporting tower 10 is made up of two superposed tower variations,namely a tubular tower 10A and a lattice tower 10B. The tower 10 bearsan equipment nacelle 30 which is rotatable about the vertical tower axisand which supports a rotor 20 bearing at least one rotor blade 22 havinga blade tip 23 and being rotatable about a substantially horizontalaxis. This view shows a three-blade rotor, the horizontal plane of therotor blade tip 23 in its lowermost position being denoted by a dashedline 25.

Besides the rotor bearing, the equipment nacelle 30 conventionally alsocontains a generator, a gear unit where called for, a wind trackingsystem, various electric components and further accessory systems. Suchparts are omitted for the sake of clarity.

Because of transportation, the tubular tower 10A is fitted with severalflange connections 12A. In the state of the art, these flangeconnections are unilateral, in general inward pointing annular flanges.In the state of the art, only the lowest flange is designed as a Tflange (double row flange pointing inward and outward) as the transitionmeans to the pedestal 18B.

In the embodiment variation of a lattice tower 10B, the transition tothe annular flange of the equipment nacelle is conventionallyimplemented by a relatively short transition unit 14B called “pot”, i.e.a “stub”. The lattice tower in general rests by each corner posts 11B ofindividually built pedestals 18B.

The graphically superposed tower variations, namely the tubular tower10A and the lattice tower 10B, show by means of the horizontal planetangent to the lowest position of the rotor blade tip(s) 25 that thedistance (blade clearance) between the blade and the tower issubstantially smaller for the lattice tower 10B and hence much morecritical than for the tubular tower 10A.

FIG. 2 is an overall view of a wind-driven power-plant where the towerdesign is that of the present invention. As in FIG. 1, the references 20and 30 respectively denote the rotor and the equipment nacelle. In itslower segment 41, the tower 40 is a lattice tower 42 which, in the shownembodiment, is fitted with four corner posts 43 and a plurality ofdiagonal struts 44, and in the upper segment 46, the tower is asubstantially tubular tower 47.

The connection of the lattice tower 42 to the tubular tower 47 takesplace in a transition range designed in a manner that the latticetower's cross-section is optimally matched with respect to forcedistribution in the tubular tower “Optimized force distribution” hereindenotes a design which, either by means of a continuous change ingeometry creates a gentle geometric transition between the variouscross-sectional shapes of the upper and lower tower segments and henceaverts force peaks in the transition zone, and/or, by means of suitableribs and/or struts, shunts force peaks present in said transition rangeinto the hookup construction. The assumption of a valid forcedistribution is vertical length—once the tower is erected—of saidtransition zone which is equal at least to the length of the radius ofthe lower tubular tower diameter and/or the use of supporting elements(shells, ribs, struts) which substantially connect the corner posts ofthe lower lattice tower to the upper tubular tower wall.

In the embodiment shown, the transition zone is configured in such a waythat a transition unit 50 is mounted directly underneath the horizontalplane 25 of the rotor blade tip 23, said unit's horizontal expanse beingconsiderably larger (more than 50%) in the lower region 70 than in theupper region 60.

The tubular wall slant of the upper tower segment 46 is slight in itslower region relative to the vertical and is denoted by a. Similarly,the slant of the upper region of the corner posts 43 of the latticetower 42 in the lower tower segment 41 is denoted by β.

In an optimal lattice tower segment, the corner posts 43 are at a slantselected in a manner that they intersect one another at a conceptualextension of these posts (shown in FIG. 2 by a dashed line) at a virtualintersection point VS. In the shown embodiment, the position of thevirtual intersection point is configured in a region extending, as seenfrom the nacelle, a third of the tower length downward. Depending on thecombination of transverse force and bending torque in the anticipated,size-determining load, the optimal virtual intersection point also maybe located above the nacelle.

The mean slant y of the transition unit 50 is defined as the anglesubtended between the vertical and a conceptual line from the maximumhorizontal expanse in the upper region 60 to the maximum horizontalexpanse in the in the lower region 70.

In the shown and especially advantageous embodiment of the invention,the angle γ is substantially larger than the slant β of the lower towersegment 41 and also than the slant a of the upper tower segment.

Conceivably too, the individual corner posts may be bent and therebyassume different slants from which a mean slant of the corner postsmight be defined similarly to the case of the transition unit.

FIG. 3 is a detailed view of a possible embodiment variation of thetower of the invention which comprises a cast, multi-part transitionunit. A sideview is shown on the right of the line of symmetry, whilethe left portion of FIG. 3 is a vertical section. The lattice tower 42is shown cropped and constitutes the lower tower segment, essentiallyconsisting per se of four corner posts 43 and diagonal struts 44. Thetubular tower 47, also shown cropped, and its walls 48 constitute theupper tower segment.

One embodiment mode of the transition unit 50 is in the form of a castconcrete shell with a wall 52 and arch-shaped clearances 53. In itsupper region 60, the transition unit is connected by a flange connector61 to the tubular tower 47 and, in its lower region 70, by four junctionplates 71 to the corner posts 43 of the lattice 42.

In the upper region 60 of the transition unit 50, the wall 52 smoothlymerges into an annular, two-row screw flange 64. The wall 48 of thetubular tower 47 is welded to a T flange 62 which, by means of an innercircle of screws 66 and an outer circle of screws 68, is screwed to theflange 64 of the transition unit 50. The inner set of screws 66 is aconventional steel construction feedthrough system, whereas the outerset of screws 68 of this embodiment mode is a blind hole screw systembecause in this manner the thickness distribution of the wall 52 of thetransition unit 50 is especially advantageous for optimal forcedistribution. Obviously, the wall 52 of the transition unit 50 may beextended slightly further outward whereby the outer screw affixationsystem 68 also can be implemented as a feedthrough screw affixationsystem. In this case however, the transition unit 50 will be somewhatheavier and hence somewhat more expensive.

In the lower region 70 and at four connection sites 72, the wall 52merges into the corner posts 43. The connection is implemented by ajunction plate system 71 using an external plate 76 and an inner plate78 that are screwed by a plurality of bolts to the connection site 72and to the corner post 43. The slants of the connection site 72 and ofthe upper region of the corner post 43 being identical, planar platescan be used as the junction plates 76, 78.

Regarding reducing the number of parts, a further embodiment mode of theinvention provides directly screwing the corner posts 43 to theconnecting sites 72 of the transition unit 50. However, in thisembodiment the force distribution from the corner post 43 into the wall52 of the transition unit 50 is slightly less advantageous.

To rigidify the lower region 70 of the transition unit 50, horizontalsupports 45 are affixed between the four corner posts 43. These postsmay selectively connect the adjacent corner posts 43 or also themutually opposite corner posts 43 and hence the diagonals of the latticetower 42. Where called for, both designs may be used jointly in order toattain especially rigid and hence advantageous construction.

For the sake of simplicity, the connection between the diagonal struts44 and the horizontal supports 45 to the plate junction 71 has beenomitted. However such connections are adequately known in the state ofthe art, for instance when joining multi-part corner posts.

For an outer diameter of 4.3 m of the T-flange 62 of the tubular tower47, the shown transition unit 50 subtends a transportation height alsoof 4.3 m, the lower transportation width being about 7 m. Suchdimensions allowing only limited transportability, a preferredembodiment mode of the invention provides that the transition unit 50 becomposed of several parts. For that purpose, the transition unit 50 issubdivided by a vertical partition plane into a left sub-unit 57 and aright sub-unit 58. The sub-units 57, 58 are joined to each other byscrew flanges 56. As an alternative to the screw flange 56, anadvantageous further embodiment of the invention uses plate junctions toconnect the sub-units 57, 58 of the transition unit 50.

Said sub-division lowers transportation costs when the two-sub-units 57,58 are laid flat up to a height of transportation of about 3.5 m at awidth of about 4.3 m so that transportation, within Germany at least,shall be problem-free.

An especially advantageous embodiment of the invention sub-divides thetransition unit symmetrically to the center line into four sub-units,making it possible either to attain even lesser transportationdimensions or to transport easily even larger transition units. Wherethe transition units are substantially larger, the inventionadditionally sub-divides the transition unit about a horizontal plane.

The shown embodiment mode of the transition unit as a cast unit offersthe advantage that the wall 52 can be fitted in problem-free manner witha variable thickness, enabling very effective use of material. Thehighly loaded regions, such as the convex transition to the annularflange 64, or the connection site 72 in the form of a plate junction 71to the corner post 43 of the lattice tower 42, may be provided withthicker walls than less-loaded regions. Also the boundary of thearchshaped clearance 54 may be fitted for instance with a rigidifyingrib. Cast construction furthermore allows optimal and smooth forcedistribution in the transition from the circular cross-section in theupper region 60 of the transition unit 50 to the illustratively shownsquare cross-section in the lower region 70 of the transition unit 50.

Where the tower design of the present invention is applied offshore, thespace available in the transition unit may be used advantageously andefficiently to receive for instance electrical drive means (converters,switching equipment, transformer), a spare parts storage bin, optionallya small workshop) or as an emergency shelter for maintenance personnelor even a visitor room. For that purpose the present support structuremay be completed by means of additional walls into a closed space whichobviously would be fitted with the required emergency access/exitfacilities and where called for with windows and climate control means.Regarding configuring the electric drive means within the transitionunit, an especially advantageous embodiment of the invention installsthem in the transition unit already at the manufacturing plant, andtests them there, and transports the transition unit together with theintegrated means as a so-called power module and then to the erectionsite.

FIG. 4 is a detailed view of a further embodiment of the transition unitof the invention which in this instance is manufactured by welding. Thelower drawing of FIG. 4 is a top view of the transition unit 50 and theupper drawing shows a vertical cross-section of the transition unitalong the line A-B.

The basic design being very similar to that of FIG. 3, already discussedcomprehensively above, essentially only differences will be discussedbelow.

The wall 52 of the transition unit 50 is a constant-thickness metalplate which is rolled inward in the upper region and which, in the lowerregion 70, is canted to the geometry of the corner posts 43.

The mean slant y of the transition unit 50—defined as the anglesubtended between the vertical and a conceptual line from the maximumhorizontal expanse in the upper region 60 to the maximum horizontalexpanse in the lower region 70—is substantially larger than the slant ofthe corner posts 43 of the lattice tower 42 and of course also largerthan that of the tubular tower since latter is cylindrical in the shownembodiment.

Using a cylindrical tubular tower allows economical manufacture; it ispossible solely because the lattice tower is made very rigid, wherebythe overall structure can be made sufficiently rigid even when foregoingwidening the tubular tower to increase rigidity. A cylindrical tubulartower is especially appropriate when the azimuth bearing the nacellebeing rotatably mounted on the tower) is selected to be very largebecause this selection allows making the tubular tower very rigidwithout widening it.

In order to easily carry out the construction by welding, the junctionplate 72 subtends in the lower region 70 of the transition unit 50 aslant that differs from that of the corner posts 43. As a result, theconnection is implemented using junction plates 76 that are selectedthick enough to absorb the forces arising from deflecting the appliedloads. The bent junction parts may be thick metal-plate and, wherecalled for, welded steel plate; however a further embodiment of theinvention also uses cast metal junction plates.

Because said force deflection warps the junction plate connectionsinward (toward the tower axis), the invention provides thick horizontalsupports 45 diagonally between every two mutually opposite corner posts43. (For simplicity, the lower part of FIG. 4 only shows one suchsupport 45 by dashed lines). In this manner, the deflection of theforces can be reliably controlled, the construction costs beingsubstantially lower, though the weight is somewhat larger, than for castconstructions.

A further embodiment of the invention rigidifies the arch-shapedclearances 53 just as for the case of cast construction, this embodimentbeing implemented in an especially advantageous manner in the form of aweld-affixed strip 55 of metal plate (as for a door frame). This weldingembodiment offers the advantage of lower manufacturing costs whenproducing only a few finished products, and simplifyingmonitoring/checking by official inspectors.

FIG. 5 is the geometric development of the transition unit of FIG. 4.The highly advantageous structural shape can be manufactured very simplyfrom the baked metal plate as one piece or preferably, in the shownillustration of the lattice tower, in four pieces with four corner posts(indicated by dashed lines). The metal plate(s) are rolled conically forthat purpose, additional edges being advantageous in the transitionregion to the corner posts to assure good transition to these posts. Ifsufficiently large rolling equipment is unavailable, the essentiallycircular shape at the transition to the upper flange also may befashioned by a plurality of smaller edges.

1. A tower (40) to support a wind-driven power-plant comprising anequipment nacelle (30) affixed to the tower (40) and a rotor (20)resting on the equipment nacelle in a manner to be rotatable about asubstantially horizontal axis, said rotor being fitted with at least onerotor blade (22), said tower comprising an upper, tubular tower segment(46) which is connected in a transition zone to a lower tower segment(41) in the form of a lattice tower (42), said lattice tower comprisingat least three corner posts (43) wherein the upper tower segment (46)constitutes at least one sixth of the entire tower, and wherein thecross-section of the lower tower segment (41) underneath the transitionzone is larger than the cross-section of the upper tower segment (46),and in that the transition zone is designed in a manner that thecross-section of the lower tower segment is matched in a force-optimizedmanner to the cross-section of the upper tower segment.
 2. Thewind-driven power-plant tower (40) as claimed in claim 1, wherein thevertical expanse of the transition zone is at least half the upper towersegment's diameter in the transition zone or immediately adjoining it.3. The wind-driven power-plant tower (40) as claimed in claim 2, whereinthe transition zone tapers upward from the cross-section of the lowertower segment (41) as far as the cross-section of the upper towersegment (46).
 4. The wind-driven power-plant tower (40) as claimed inclaim 1, wherein the transition zone is constituted by a transition unit(50) comprising a lower region (70) connectable to the lower towersegment (41) and an upper region (60) connectable to the upper towersegment (46).
 5. The wind-driven power-plant tower (40) as claimed inclaim 4, wherein the transition unit's lower region (70) is designed ina manner that its largest horizontal expanse is 50%—larger than itshorizontal expanse in the upper region (60),
 6. The wind-drivenpower-plant tower (40) as claimed in claim 4, wherein the tower (40) isdesigned in a manner that the transition unit (50) is configuredunderneath a horizontal plane (25) defined by a blade tip (23) when therotor blade (22) is down in the vertical.
 7. The wind-driven power-planttower (40) as claimed in claim 4, wherein the upper region (60) of thetransition unit (50) is designed in a manner that the transition unit(50) is connected by a detachable connection means (61) to the uppertower segment (46).
 8. The wind-driven power-plant tower (40) as claimedin claim 4, wherein the lower region (70) of the transition unit (50) isdesigned in a manner that the transition unit (50) can be connected witheach corner post (43) of the lattice tower (42) by means of a detachableconnection means (71).
 9. The wind-driven power-plant tower (40) asclaimed in claim 7, wherein the detachable connection means (61) betweenthe upper region (60) of the transition unit (50) and the upper towersegment (46) comprises a two-row screw flange (64) mounted on thetransition unit (50) as the connection site and a T-flange (62) mountedon the upper tower segment (46).
 10. The wind-driven power-plant tower(40) as claimed in claim 4, wherein the lower region (70) of thetransition unit (50) comprises connection sites (72) for plate junctions(71) to the corner posts (43) of the lattice tower (42).
 11. Thewind-driven power-plant tower (40) as claimed in claim 4, wherein abuilt height of the transition unit (50) is limited by the overpassheight beneath bridges and is between 4 and 5.5 m.
 12. The wind-drivenpower-plant tower (40) as claimed in claim 4, wherein the transitionunit (50) consists of at least two sub-units (57, 58) preferablydetachably connected to each other at a connection site
 56. 13. Thewind-driven power-plant tower (40) as claimed in claim 12, wherein thetransition unit (50) comprises at least one vertical partition plane.14. The wind-driven power-plant (40) as claimed in claim 12, wherein thetransition unit (50) comprises at least one horizontal partition plane.15. The wind-driven power-plant tower (40) as claimed in claim 12,wherein the transition unit (50) or a sub-unit (57, 58) of thetransition unit (50) is designed in a manner that, by means of adapterelements which are mounted on the extant connection sites (56, 64, 72)or on connection sites of their own for that purpose, said unit orsub-unit can be transported on a low-loader trailer.
 16. The wind-drivenpower-plant tower (40) as claimed in claim 12, wherein the transitionunit (50) or the sub-units (57, 58) of the transition unit (50) is/aredesigned in a manner that the transportation of several transitionunit(s) (50) or transition sub-units (57, 58) connected directly orindirectly to each other can be carried out by a low-loader trailer. 17.The wind-driven power-plant tower (40) as claimed in claim 4, whereinthe transition unit (50) comprises a wall (52) and is made in the shellmode of construction.
 18. The wind-driven power-plant tower (40) asclaimed in claim 10, wherein the basic shape of the transition unit (50)is substantially a markedly conical tube, the mean slant (y) of theconical tube (52) relative to the center axis being larger than that (a)of a wall (48) of the lower region of a tubular tower (47) and/or thanthe slant (β) of the upper region of the lattice tower corner posts(43).
 19. The wind-driven power-plant tower (40) as claimed in claim 18,wherein the mean slant (γ) of the wall (52) of the transition unit (50)relative to the center axis is more than 25°.
 20. The wind-drivenpower-plant tower (40) claimed in claim 4, wherein the transition unit(50) smoothly merges, from a substantially circular cross-section in theupper region (60), into a polygonal, preferably triangular or tetragonalcross-section in the lower region (70).
 21. The wind-driven power-planttower (40) as claimed in claim 18, wherein the wall (52) of thetransition unit (50) is fitted with at least one clearance (53).
 22. Thewind-driven power-plant tower (40) as claimed in claim 21, wherein theminimum of one clearance (53) is archway-shaped and in that thisarchway-shaped clearance (53) runs from corner post (43) to corner post(43).
 23. The wind-driven power-plant tower (40) as claimed in claim 22,wherein the minimum of one archway-shaped clearance is fitted withribbed or archway-like rigidifying means (55).
 24. The wind-drivenpower-plant (40) as claimed in claim 4, wherein horizontal supports (45)are configured in the lower region (70) of the transition unit (50)between the corner posts (43) of the lattice tower (42) and connect toeach other the adjacent corner posts (43) and/or the (diagonally)opposite corner posts (43).
 25. The wind-driven power-plant tower (40)as claimed in claim 4, wherein the lattice tower (42) comprises at leastfour corner posts (43) and the transition unit (50) is fitted with ribsbracing the lines of connection of mutually opposite corner posts (43)(diagonals).
 26. The wind-driven power-plant as claimed in claim 4,wherein the transition unit (50) is a cast sub-assembly.
 27. Thewind-driven power-plant tower (40) as claimed in claim 18, wherein thewall (52) of the transition unit (50) curves convexly when seen invertical cross-section.
 28. The wind-driven power-plant tower (40) asclaimed in claim 27, wherein the slant of the connection sites (72) inthe lower region (70) of the transition unit (50) corresponds to theslant of the upper region of the corner posts (43) of the lattice tower(42).
 29. The wind-driven power-plant tower (40) as claimed in claim 4,wherein the transition unit (50) is a welded sub-assembly.
 30. Thewind-driven power-plant tower (40) as claimed in claim 1, wherein thetower segment (41) in the form of a lattice tower (42) comprises severalsuperposed sections and that one section each time comprises the cornerposts (43) and at least one strut means (44) runs diagonally between thecorner posts.
 31. The wind-driven power-plant tower (40) as claimed inclaim 30, wherein the slope of the diagonal strut means is identical inall sections.
 32. The wind-driven power-plant tower (40) as claimed inclaim 1, wherein cables connecting said power-plant to an electricalgrid run inside the corner posts (43) designed as hollow constructionshapes.
 33. The wind-driven power-plant tower as claimed in claim 32,wherein cable-protecting pipes receiving the cables run inside thecorner posts (43).
 34. The wind-driven power-plant tower as claimed inclaim 1, in the form of an upper, substantially tubular tower segmentand of various lower tower segments in the form of a lattice tower,wherein the total tower height is variable by selecting differentlattice tower heights.